This invention relates to a transformer suitable for use in high frequency appliances and more specifically, the invention is directed to reduce the number of manual steps in producing the transformer, to make possible production of the transformer by greater use of machines so as to reduce the cost of production and to provide the products having uniform characteristics.
FIG. 1 illustrates diagrammatically an example of the conventional balance-unbalance conversion transformer for use in the range of a VHF band to a UHF band.
FIG. 1 is a perspective view of the conventional transformer and FIG. 2 is its equivalent circuit diagram. As is obvious from FIG. 2, a signal source 13 and a signal source impedance 14 are connected to the input terminals 1a, 2a of a first transformer T.sub.1 so as to convert an unbalanced signal into a balanced signal by the first transformer T.sub.1. Input terminals 5a, 8a, 6a, 9a of a second transformer T.sub.2 are connected to the output terminals 1b, 2b of the first transformer T.sub.1. This second transformer T.sub.2 effects the impedance conversion at a ratio of 1:4. A load 15 is connected to the output terminals 5b, 9b of the second transformer T.sub.2.
In other words, a value four times the signal source impedance 14 appears as a value at the load 15.
In FIG. 2, further, the input terminal 2a of the first transformer T.sub.1 is grounded and the junction between the output terminals 6b, 8b of the second transformer T.sub.2 is grounded.
When the load 15 is a balance mixer diode or the like, the output terminals 6b, 8b are not grounded but are used as the input terminals of a local oscillation signal.
As depicted in FIG. 1, the transformer comprises the first transformer T.sub.1 which is formed by winding a paired wire 3 consisting of copper wires 1 and 2, that are insulation-coated in parallel and in intimate contact with each other, on a ring-like toroidal core 4 and the second transformer T.sub.2 which is formed by winding a paired wire 7 consisting of copper wires 5 and 6, that are insulation-coated in parallel and in intimate contact with each other, as well as a paired wire 10 consisting of copper wires 8 and 9, that are insulation-coated in parallel and in intimate contact with each other, on another ring-like toroidal core 11. The start and end of each of the paired wires 3, 7, 10 are bonded to the toroidal cores 4, 11, respectively, by use of an adhesive 12 in order to prevent them from getting loose and rewinding. One end each of the copper wires 1, 2, 5, 6, 8, 9 of each of the paired wires 3, 7, 10 is used as the input terminal 1a, 2a, 5a, 6a, 8a, 9a while the other end each of the copper wires is used as the output terminal 1b, 2b, 5b, 8b, 9b. The output terminal 1b of the copper wire 1 of the first transformer T.sub.1 is wired to the input terminals 5a, 8a of the copper wires 5, 8 of the second transformer T.sub.2 and the output terminal 2b of the copper wire 2 of the first transformer T.sub.1 is connected to the input terminals 6a, 9a of the copper wires 6, 9 of the second transformer T.sub.2. Furthermore, the output terminals 6b, 8b of the copper wires 6, 8 of the second transformer T.sub.2 are connected to each other.
In the conventional transformer having the construction described above, the paired wires 3, 7, 10 are wound on the ring-like toroidal cores 4, 11 so that winding must be made manually and automation is difficult to attain. This is because high frequency appliances generally use toroidal cores 4, 11 having an inner diameter as small as about 2 mm and a practical automatic winding machine for winding such an extremely small core has not yet been available.
Since the paired wires 3, 7, 10 must be wound manually, the winding pitch does not become uniform but causes non-uniformity, resulting in variance in the characteristics of the products. Furthermore, since the two transformers T.sub.1, T.sub.2 are produced by winding separately the wires on the two toroidal cores 4, 11 and then connecting the transformers by use of a large number of wires, productively is extremely low and hence, the production cost becomes inevitably high.